Control apparatus



Ill-

Nov. 13, 1962 J F' SCHUGT 3,064,171

CONTROL APPARATUS Filed Deo. 27. 1960 coNTRoI. SIGNAL I AMPLIFIER I l I INVENTOR.

JOSEPH E SCHUGT B ATTORNEY United States Patent M 3,064,171 CONTROL APPARATUS Joseph F. Schugt, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Filed Dec. 27, 1960, Ser. No. 78,664 1t) Claims. (Cl. S18-207) This invention relates to servomotors, and more particularly to means for reducing the heat in two phase servomotors.

When A.C servomotors are used to maintain such devices as stable platforms level they normally produce so much heat that they cannot be enclosed `with the platform. This heat is due to the fact that the servomotor must have linear torque vs. control current characteristic, which requires a constant excitation of one phase of the motor strong enough to result in maximum required torque with a given maximum control current in the other phase, and the motor must be large enough to right the platform from any excursion it may take. Although the servomotor is large enough to right the platform after its greatest possible excursion it is not used at its full capacity most of the time because the platform is normally approximately level. However, the size of the servomotor may not be reduced or the time it takes to level the platform after a large excursion will be too long.

lIn a two phase servomotor one phase is generally known as the excitation phase and the other phase is known as the control phase. Normally there is an excitation current to the excitation phase winding at all times, and a signal known as a control signal when applied to the control phase winding causes the motor to produce the desired amount of torque. This control signal normally comes from a condition responsive means which is attached in some manner to the device to be controlled. The current from the condition responsive means is generally small and therefore is applied to a control signal amplifier the output of which is applied to the control phase winding. The torque of the motor is proportional to the product of the excitation current and the control current. However, due to the inherent resistance of the coils there is an 12R loss or heat produced in the motor at all times that excitation current is flowing whether the motor is producing torque or not.

To reduce the heat in the motor due to the excitation current the present invention provides two levels of excitation current. This is, however, just in the preferred embodiment herein disclosed and it should be remembered that a number of different levels may be used depending upon the use of the motor. When two levels of excitation current are used a simultaneous complimentary change in the control signal amplifier gain has to occur |whenever the excitation is changed from one level to another so as to keep the product of excitation current and control signal amplifier gain constant. For instance, if the low level excitation current is decreased to onehalf of its nominal value the control signal amplier has to deliver a control phase current of twice the value that would normally be applied to the control phase winding. In this way, the desired torque vs. input signal proportionality can be maintained through the whole range from maximum negative to maximum positive torque, and the switching step procedure will have no effect whatsoever upon the control loop dynamics, while the heat produced in the motor can be easily reduced to a fraction of what it is with the excitation current full on all the time. The switching process from one excitation level to another is done automatically in the following manner. A condition responsive means which may be a movement to the excitation phase of the servomotor.

3,064,171 Patented Nov. 13, 1962 ICC sensor is placed on the object to be controlled by the servomotor, this could be, for example, a gimbal on a stable platform. The output of this sensor is applied to a signal conditioning means, which in this preferred embodiment is a Voltage divider, and simultaneously to an amplitude discriminator amplifier. The discriminator amplifier activates either of two coils of a relay, which control two arms and their associated contacts. One coil pulls both arms in one direction when a signal exceeding a predetermined amplitude is applied to the discriminator amplifier and the other coil returns them both to their original position `when the signal is removed.

One of the arms serves to normally shunt a portion of the Ivoltage divider thereby changing the effective amplification of the control signal amplifier connected to the control winding of the servomotor. When the rst relay coil is energized and the second coil is deenergized a portion of the voltage divider remains shunted and the control signal amplifier circuit has normal amplification, but when the second relay coil is energized and the first coil deenergized both arms are pulled into the other position and the full voltage divider is in the circuit lowering the effective amplification of the control signal amplifier. The effective amplification is lowered in accordance with the amount that the excitation current is raised. For example, if the excitation current is raised from one half to full current the effective amplification of the control signal amplifier is lowered from normal amplification to one half. The other arm of the relay coil serves to put half or full excitation power on the excitation phase by controlling a second signal conditioning means which in this preferred embodiment is a transformer with a tap for a lower voltage. When the first Irelay coil is activated the arm is in the position which puts half power on the excitation phase and when the second relay coil is activated the arm is in a position which puts full power on the excitation phase.

Thus, when the device to be maintained in a given position deviates from this position by some large amount the sensor produces a signal which is applied to the control signal amplifier and simultaneously applied to the discriminator amplifier. This larger signal is passed by the discriminator amplifier and activates the second relay coil pulling both arms in to the activated position. Thus half power is applied from the control signal amplifier to the control winding and full power is applied When the servomotor rights the object or brings it back to the desired position the sensor no longer produces a large signal, the discriminator amplifier allows the first relay coil to become energized, and the two arms are pulled back into their normal positions. The control signal amplifier again has a normal signal in the case of small excursions or no signal for no excursions and the excitation phase again has half power applied to it.

It should be noted that the relay described herein and explained more fully below is simply the control means used in this preferred embodiment. Any control means could be used which would respond to the condition responsive means and function to control the two signal conditioning means. Other control means which might be used could include semiconductor switches.

Thus, the motor is given full excitation power only when it is actually needed, and at times when the motor is not working or when a much smaller motor could be used, the motor only has half excitation andthe heat is cut down to a mere fraction.

Accordingly, it is an object of this invention an improved control apparatus.

Another object of this invention is to provide a servomotor with very low heat production.

to provide Another object of this invention is to provide a servomotor with very low power dissipation.

These and other objects of the present invention will be understood upon consideration of the accompanying speciication, claims, and drawing of which the single FIGURE is a schematic diagram of the preferred embodiment of this invention.

In the FIGURE the numeral designates a control sensor or movement sensor. This sensor is made up of three windings a primary winding designated number 11 which is connected from a terminal 16 to ground and two secondary windings designated 12 and 13. Terminal 16 is adapted to have an A.C. voltage applied to it which Well -may be the excitation voltage for the two phase servomotor. This excitation voltage will be explained later. Secondary windings 12 and 13 are connected in series between a junction point designated numeral 14 and ground. Secondary windings 12 and 13 are connectedV so that any voltages induced into them from the primary winding are opposing in these windings. A movable member, composed of magnetic material, designated number 15 is mounted, by means not shown, so that in the normal position an equal amount of tlux connects the primary winding 11 and the. secondary winding 13 and the primary winding 11and the secondary winding 12. When the movable member 15 is in. the normal position the flux linkages between the primary 11 and the two secondary windings 12 and 13 are equal and the voltages induced into the secondary windings 12 and 13 exactly cancel each other out. However, if a movement of the apparatus to which the sensor 10` is connected should cause the. movable member 15to Vshift to the left there would be. moreV liux linkage between primary winding 11 and secondary winding 12 and less ilux linkage between primary winding 11 and secondary winding 13 causing a new voltage. to appear on junction point 14. Also, a shift to the, right would cause more voltage to be induced into secondary winding 13, causing a net voltage on junction point 14. It should be noted that the control sensor 10 is simply a device which could` be used if movement was the. condition to be sensed. However, any condition responsive means might be used which would indicate the condition which itY was desired to control, or otherwise respond to, for example, a temperature sensing device, aV pressure sensing device, or alight sensing device.

Numeral designates an amplitude disoriminator amplifier circuit consisting of a first stage of amplication,Y

transistor 21 and its associated circuitry, and two stages of power amplification, transistor 22 and its associated circuitry and transistor 23 and its associated circuitry. Transistor 21 has an emitter 24, a collector 25, and a base 26.. Emitter 24 is connected directly to ground. Collector 25l isconnected by means of a resistor 27 to a junction point 17 which is adapted to have a positive voltage supply connected to it. The base26 of transistor 21 is connected toY ground by means of a resistor 28 and to junction point 17 byv means of a resistor 29. Acapacitor 30 is connected from junction point 14 to the base 26 of transistor 21. A diode 33 is connected from collector 25 of transistor 21 toa junction point 34. A capacitor 35 connects junction point 34 to junction pointV 17 and a resistor 36 is connectedbetween junction point 34 and another junction point 37. A capacitor 38 connectsk junction 37 to junction point 17.

` Transistor 22 has an emitter 40, a collector 41, and al base Y42. Base 42 is connected directly to junction point 37. Emitter 40 of transistor 22 is connected to ground base 52. Base 52 of transistor 23 connects torcollector 41 of transistor22 throughy a. resistor 53.' A resistor S4 is. connected from base 52 of transistor 23 `to ground.

- through a resistor 43. A relay coil 44 is connected be- Emitter 500i transistor 23 connects directly to emitter 40 of transistor 22. A relay coil 5S is connected 'from collector 51 of -transistor 23 to junction point 17 and has a diode 56 in parallel with it.

Relay coils 44 and 55 are portions of the same relay. This relay also has two arms and their associated contacts. These por-tions of the relay are designated number 66 and 70. Portion 61) has an arm 61 and two contacts 62 and 63, and portion 70 has an arm 71 and two contacts 72 and 73. When relay coil 55 is energized it holds the relay portions numbered 60 and 7 tl in the position shown. That is, arm 61 of portion 60 is touching contact 62 and arm 7.1 of portion 70 is touching contact '72. Discriminator amplifier circuit 20, as will be seen later, is so designed that when relay coil 55 is energized relay coil 44 is deenergized and vice versa. When relay coil 44 is energized and relay coil 55 is deenergized arm 61 of relay portion 6d is touching contact 63, and arm 71 of relay portion 70 is touching contact 73. A resistor 65 is connected froml relay arm 61 of relay portion 6i) to ground. A resistor 64 is connected from contact 62 of portion ett to relay arm 61.k Contact 62 of relay portion 60 is also connected to junction point 14.

The two phase servomotor which is to be controlled is numerically designated 75. Servomotor 75 has a rotor 76, a Vcontrol winding 77, and an excitation winding 78. Control winding 77 is energized by the output of a control signal amplifier designated number 79. One input terminal of the control signal amplifier 79 is connected to relay arm 61 of portion tl'and the other terminal is connected to ground. A transformerl has a primary winding 82 and a secondary winding 81. One side of secondary winding 81 is connected to one side of excitation winding 78 of servomotor 75. The other side ot secondary winding 81 of transformer 80 is connected to contact 73 of relay portion 70. Secondary winding 81 of transformer S0 is tapped oi -at a lower Voltage point designated 83 and this point is connected to contact 72 of portion 7 0- of the relay.'V The arm 71 of portion 70` of the relay is connected to the other side of the excitation winding 7 8 of servomotor 75. One side of the primary winding 82 of transformer 80 is connected to ground and the other side is connected to a terminal 84 through a capacitor'. Terminal 84 is adapted to have an excitation voltage applied to it. Capacitor 85iis merelypa phase shifting capacitor in the event that terminal 84 and terminal 16 are connected together to utilize one power supply.l

j Operation j In this preferred embodiment assume that se-rvomotor 75 is utilized to maintain level a gimbal, on which is mounted control sensor 10. Resistors 28 and. 29 form a bias network for transistor 21 which maintainsfthe `base 26 in a positive or conducting condition. The amount of negative signal required on base 26 to cut off transistor 21 determines the excursion which control sensor 10. and hence the gim-bal may take. In Vother Words, assume that control sensor 10 is only tilted slightly 'to the right. Movable member 15 causes -a slightly larger lux linkage between Vprimarly 11 and secondary 113 than there is between primary 11 and secondary 12. Thus, a net A.C. voltage will be applied to junction point 14. This net A.C. voltage will beY applied through capacitor 30 to the base 26 of transistor 21. However, lbecause the negative going por-tions of the cycle are not of large enough magnitude to cut transistor 21 oit this signal has no elect on discriminator .amplifier 20. Tran-` sistor 23, which is'normally conducting, continues to conduct maintaining relay coil 55 energized. Thus, arm 61 ofr relay portion 60 and arm 71 of relay portion 70 remain in the position in which they are shown.

-Ifpcontrol sensor 10 should take a large excursion causing movable portion 15 to move either to the left or the, right far enough to cause a net A.C. voltage Von junction point 14, which is larger than the positive bias ade-1,171

predetermined by the ratio of resistor 29 and resistor 28, rthe negative portions of the signal will cause transistor 21 to cut off. As transistor 21 cuts off on the negative portions of the incoming signal collector 25 of transistor 21 will go positive. These positive pulses will be applied -to the lter network consisting of capacitor 35, capacitor 38, and resistor 36. The filter network will tend to make the D.C. pulses from the collector 25 of transistor 21 appear as a steady D.C. signal which is applied to the base 42 of transistor 22. This steady DC. signal on base 42 of transistor 22 will cause transistor 22 to conduct, energizing relay coil 44. As transistor 22 turns on collector 41 tends to go negative. This negative going signal is applied to base 52 of transistor 23 through resistor 53. As the negative going signal is applied to base 52 of transistor 23, transistor 23 turns off deenergizing relay coil 55.

i When relay coil 44 is energized, relay coil 55 is deenergized, arm 61 of relay portion 6G is switched to contact 63 and arm 71 of relay portion 70 is swi-tched to contact 73. Thus, the excitation winding is switched from the lower voltage which is on contact 72 to the higher voltage which is on contact "73 applying a larger excitation to the excitation winding 7S of servomotor 75. Simultaneously the shunt is taken away from' resistor 64. Thus, resistor 64 is effectively put in series with the signal from junction point '14 being applied to the control signal amplifier. This causes the signal to be reduced the exact amount which the excitation phase is raised. For example, if the tap 83 of secondary winding 81 is a center tap, when arm 71 is on contact 72 excitation winding 78 has exactly half of the excitation voltage that it will have if arm 71 is touching contact 73. In this case, resistor 64 and resistor 65 would be of the same size, and when resistor 64 is shunted by arm 61 touching contact 62 of relay portion 60 the control signal amplifier would effectively have twice the amplification as it does when resistor 64 is in the circuit. Thus, it can be seen that when the device to be maintained level by servomotor 75 takes a large excursion the excitation winding receives more excitation voltage and the control signal is reduced. In this manner the speed remains the same but the torque capability is increased so that the motor may take care of the larger load. That is, the proportionality between the signal from the control sensor and the torque of servomotor 75 is maintained.

Thus, at times when the servomotor 75 is not needed or when only a small amount of torque is required the excitation voltage on the excitation winding 78 is reduced to a lower val-ue thus lowering the 12R losses or heat losses to a mere fraction of what they are when the servomotor 75 has full excita-tion voltage applied to the excitation winding. However, as soon as more torque is needed from servomotor 75 a larger excitation voltage is appliedl While I have shown and described a specific embodiment of this invention, further modification and improvements will occur to those skilled in the art. I desire it lto be understood, therefore, that this invention is not limited to the particular form shown and I intend in the appended claims to cover all modification which do not depart from the spirit and scope of this invention.

What i claim is:

1. In a servo control system: condition responsive means adapted to produce a signal indicative of a condition; a servomotor having a control winding and an excitation winding; excitation 4means connected to said excitation winding, normally exciting said excitation winding at a first level, and controllable so as to excite said excitation winding at a second level higher than said first level; control means connected to said condition responsive means to receive the signal thereof, and adapted to provide a control function for signals applied thereto equal to or greater than a predetermined level; amplifier means having an input and an output; means connecting said amplifier means output to said servomotor control winding; a resistor network including at least one resistor and means normally shunting said resistor and controllable to remove the yshunt from said resistor; means including said resistor network connecting said condition responsive means to said amplifier means input; and means connecting said control means to said excitation means and to said network so that when a signal equal to or greater than said predetermined level is applied to said control means said control means functions to control said excitation means to excite said excitation winding at said second level and to control said network to remove the shunt from said resistor.

2. In a servo control system: condition responsive means adapted to produce a signal indicative of a condition; a servomotor having a control winding and an excitation winding; excitation means connected to `said excitation winding, normally exciting said excitation winding at a first level, and controllable so as to excite said excitation winding at a second level higher than said first level; control means connected to said condition responsive means to receive the signal thereof and adapted to provide a control function for signals applied thereto equal to or greater than a predetermined level; amplifier means having an input and an output; means connecting said amplifier means output to said servomotor control winding; signal conditioning means having an input and an output and controllable to attenuate a signal applied to the input thereof; means connecting said input of said signal conditioning means to said condition responsive means and said output of said signal conditioning means to said amplifier input; and means, connecting said control means to said signal conditioning means and said excitation means so that when a signal equal to or greater than said predetermined level is applied to said control means said control means functions to control said excitation means to excite said excitation winding at said second level and to control said signal conditioning means to attenuate a signal applied to the input thereof.

3. Control apparatus comprising: motor means, said motor means having a first and a second winding; a first and a second signal conditioning means controllable to attentuate a signal applied thereto; condition responsive means adapted to produce a signal indicative of a condition; means including said first signal conditioning means connecting said condition responsive means to said first winding of said motor means; means including said second signal conditioning means connected to said second winding of said motor means and adapted to have an excitation voltage Iapplied thereto; control means connected to said condition responsive means to receive the signal thereof and adapted to provide a control function for signal-s applied thereto equal to or greater than a predetermined level; and means connecting said control means to said first and second signal conditioning means so that when a signal equal to or greater than said predetermined level is applied to said control means said control means functions to control said first signal conditioning means for greater attenuation and said Isecond signal conditioning means for less attenuation.

4. Control lapparatus comprising: motor means having a first and a second winding; a first and a second signal conditioning means controllable to attenuate a signal applied thereto; terminal means ad=apted to have one or more signals applied thereto; means including said first signal conditioning means connecting said terminal means to said first winding of said motor means; means including said second signal conditioning means connected to said second winding of said motor means and adapted to have an excitation voltage applied thereto; control means connected to said terminal means to receive a signal applied thereto and adapted to provide a control function lfor signals applied thereto equal to or greater than a predetermined level; and means connecting said control means to said first and second signal conditioning means so that when a signal equal to or greater than said predetermined level is applied to said control means said control means i functions to control said first signal conditioning Ameans for greater attenuation and said second signal conditioning means for less attenuation.

5. Control apparatus comprising: motor means having a first and a second winding; a first and a second signal conditioning means each having an input and an output and being controllable to produce a plurality'of signals at said output when a signal is applied at said input; condition responsive means adapted to produce a signal indicative of a condition; ia first amplifier means having an input and an output; -means including said first signal conditioning means connecting said condition responsive means to said input of said first amplifier means and said output of said first amplifier means to said first Winding of said motor means; means inclu-ding said second signal conditioning means connected to said second winding of said motor means and adapted to have an excitation voltage applied thereto; a second amplifier means having an input and an output; control means adapted to provide a plurality of control lfunctions -for signals applied thereto equal to or greater than a plurality of predetermined levels; means connecting said condition responsive means to said input of said second amplifier means and said control means to said output of said second amplifier means; and means connecting .said control means t-o said first and second signal. conditioning means so that when a signal equal to or greater than one of said predetermined levels is applied to said control means said control means functions to control said first'and second signal conditioning means to a predetermined one of said plurality of signals a-t said outputs.

6. Control apparatus comprising: motor means having a first and a second winding; a first and Ia second signal Conditioning means each having an input and an output and being controllable to produce a plurality of signals at said output when a signal is applied at said input; terminal means adapted to have one or more signals applied thereto; a 'first amplifier means having an input and an output; means including said fi-rst signalY conditioning to or greater than a predetermined level; amplifier means having an input and an output and controllable for a reduced amplification; means connecting said amplifier means output to said servomotor control winding and said condition responsive means to said amplifier means input; and means -connecting said control means to said excitation means and to said amplifier means so that when a signal equal to or greater than said predetermined level is applied to said control means said control means functions to control said excitation means to excite said excitation winding at saidrsecond level yand to control said amplifier means to reduce the amplification.

8. in a servo control system: terminal means adapted to have one or more signals applied thereto; a servomotor having a control winding and an excitation Winding; excitation means connected to said excitation winding, normally exciting said excitation winding at a first level, and controllable so as to excite said excitation winding at' a second level higher th-an said .first level; control means connected to said terminal means to receive theV signal thereof and adapted to provide a control function for signals applied thereto equal to or greater than a predetermined level; amplifier means having an input and an output and controllable for a reduced amplification; means connecting said amplifier means output to said servomotor winding and said terminal means to said amplifier means input; and means connecting said control means to said excitation means andto said amplifier means so that when a signal equal to or greater than said .predetermined level is applied to said control means said control means functions to control said excitation, means to excite said excitation winding' at said second level and means connecting said terminal means to said input of `said first amplifier means and said output of said first amplifier means to said first winding of said motor means; means including said second signal conditioning means connected to said second winding of said motor means and adapted to have an excitation voltage applied thereto; a second y'amplifier means having an input and an output; control means adapted to provide a plurality of control functions for signals applied the-reto equal to or greater than a plurality of predetermined levels; means connectingy said terminal means to said input of said second amplifier means and said control means to said output of said second amplifier means; and means connecting said control means to said first and second signal conditioning means so that when a signal equal to or greater than one of said predetermined levels is applied to said control means said control means functions to control said first and second signal conditioning means to a predetermined adapted for to control said amplifierr means to reduce theamplification.

9. Control apparatus comprising: motor Vmeans having a'first vand a second Winding; a first andra second signal conditioning means controllable to attenuate a signal applied thereto; terminal means adapted to have one or more signals applied thereto; means including said first Y signal conditioning means connecting said terminal means to said first Winding of .said motor means; means including said second signal conditioning means connected to said 4second winding of said motor means and adapted to have an excitation applied thereto; control means connected to said terminal means to receive a signal applied thereto andadapted to provide a .first control function Vfor signals of a first level applied thereto and to provide a second control'rfunction for signals of a second level applied thereto; and means connecting said control means to said first and second signal conditioning means'so that when a signal is applied to said control means said control means functions to control said first and .second Y signal conditioning means.

10. Control apparatus comprising: motor means, said motor means'having a first and second winding means a first and a second phase of energization; switching'means, said switching means being characterized by having at least a first Vand a second mode; means connecting said switching means to said first and second winding means so that when said switching means are in said first mode fullcurrent` will flow iny said first winding means and partial current will flow Vin sai-d second phase, and when said switching means are in said second mode partial current will flow in said first winding meansV and fulll current will flow in said second winding means; and means to actuate said switching means from said first mode to said second mode when saidrmotor means has Ya predetermined loa-d applied to it.

No references cited. 

